The demands made on such a cam disk vary greatly. On the one hand, the clutch member of the cam disk or ring must exhibit sufficient elasticity to withstand even jolt-like torques without causing fatique fracture, while conversely the front cam rolling surface must be as hard and wear-resistant as possible to withstand the extraordinarily high pressure occurring between the cam surface and the rollers. The magnitude of the piston force may be selected proportionately to the wear resistance of the cam surface material, i.e., the greater the wear resistance, the greater may be the piston force, while the torque to be transmitted should be proportionate to the elasticity of the coupling assembly which is subjected to extreme bending stress, i.e. the greater the elasticity of the coupling assembly, the greater may be the torque selected for transmission.